Overview:
Estimation is the process of approximating answers in common situations. Sometimes the exact value is not necessary, as when estimating the number of people who attend an outdoor concert. Sometimes it is easier to use approximate figures, such as when estimating the amount to add for tax or a tip. The most common forms of estimation involve rounding up or rounding down.
Estimation by Using Approximate Figures
Typically, this form of estimation is used when adding tax or a tip. Suppose sales tax is 8.8%. In order to estimate how much money is needed to make a purchase, 10% in easier to use, and will give a safer cushion. A CD costs $14.99, or almost $15.00. Ten percent of $15.00 is $1.50, so the purchase will be somewhat less than $16.50.
Estimation by Rounding Up
In the previous example, 8.8% was rounded up to 10%, and $14.99 was rounded up to $15.00. If a product is sold in packages, one will almost always have to buy more than needed to get a correct quantity. If labels are sold in packages of 100, and 1529 labels are needed, 16 packages or 1600 labels will be enough.
Estimation by Rounding Down
Most of the time, rounding down doesn’t provide a safe estimate. There are a few situations that rounding down is the more appropriate estimate. For example, many calculators truncate decimals to the preceding decimal place if the decimal answer is more than 6 places.
Estimation by Rounding to the Nearest
Sometimes it will be more practical to estimate by rounding to the nearest 10 or 100 or 1000. For example, the speed of light is about 186, 281.7 miles per second. To the nearest mile, round up to 186, 282. To the nearest 10 miles, round down to 186, 280. To the nearest 100 miles, round up to 186, 300.
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